二茚基钇-铝双金属配合物催化丙烯腈聚合

丙烯腈 (AN)聚合通常采用自由基和阴离子聚合两种 .它们存在催化剂活性低 ,用量大等缺点 .关于丙烯腈的配位聚合研究报道则较少 .最近 ,有报道发现二价稀土化合物可以催化丙烯腈聚合 ,但催化活性较低[1 ,2 ] .本文以二茚基钇 -铝双金属配合物 (C9H7) 2 Y(μ- Et) 2 Al Et2(以下以 Y- Al代表 )为 AN聚合催化剂 ,发现它单独可以催化 AN聚合 .当外加酚钠(Ph ONa)时 ,可以大大提高聚丙烯腈 (PAN)的产率及分子量 .研究了单体浓度、催化剂浓度、温度、时间等对 AN聚合的影响 ,并对其引发机理进行了研究 .Y- Al的合成及聚合方法见文献 [3…     

MICROSTRUCTURE AND FRACTAL FORMATION OF ANNEALED Ge-Au FILM AND Ge-Au/Au BILAYER FILMS

The as-deposited and annealed Ge-Au film and Ge-Au/Au bilayer films have been observed by transmission electron microscopy. The bilayer with a composition of Ge-5at%Au film is amorphous, while the Ge-22at%Au film is polycrystalline. Higher concentration of Au raises the structural heterogeneity and instability. Fractals can be observed in the Ge-5at%Au/Au bilayer samples annealed at 60-100℃. The difference of the fractal patterns generated from Ge-Au/An and a-Ge/Au films call be attributed to the higher heterogeneity and instability in Ge-Au/An bilayers.     

Adsorption of gold on low index planes of rhenium

On atomically rough areas of a thermally cleaned rhenium field emitter, adsorbed gold behaves like it does on tungsten. The average work function $\text{}\text{?}$gf increases at low average gold coverage $\text{}\text{?}$gq due to formation of gold-rhenium dipoles, and at high coverage a structural transformation in the gold layer leads to a $\text{}\text{?}$gq-independent work function. Broadly similar behaviour is found for gold on the low-index planes of tungsten, but on low-index rhenium planes gold behaves rather differently. When thermally cleaned at > 2200 K and annealed below 800 K, the work function, φ(clean), of (101&#x0304;1&#x0304;) takes one of two values 5.25 ± 0.04 eV, and 5.36 ± 0.04 eV, which are tentatively attributed to the two possible structures of this plane. Similar behaviour is expected and observed for (101&#x0304;0),but the values taken by φ(clean) are not well defined. Both forms of (101&#x0304;1&#x0304;) are thought to undergo reconstruction above 800 K forming a single structure with φ(clean) = 5.55 ± 0.03 eV. (112&#x0304;0) and (112&#x0304;2&#x0304;) each have only one possible structure, and in keeping with this, φ(clean) has a single well-defined value for each plane. The flatness of (101&#x0304;1&#x0304;) and (101&#x0304;0) leads to field reduction at their centres which produces an increase in their measured work functions by up to 10%. The initial increase in φ produced by gold condensed at 78 K and spread at low equilibration temperatures T_s on (112&#x0304;2&#x0304;), (101&#x0304;1&#x0304;) and (112&#x0304;0) is attributed to gold-rhenium dipoles, which, on the latter two planes approximate to the Topping model, giving dipoles characterised by μ₀(1011) = 0.1 × 10^?30 C-m with α = 10 ų and μ₀(112&#x0304;0) = 0.32 × 10^?30 C-m with α = 22 ų, where μ₀ is the zero-coverage dipole moment and α its polarizability. Failure of the Topping model on (112&#x0304;2&#x0304;) is attributed to its atomically rough structure. No dipole effect is seen on (101&#x0304;0). Energy spectroscopy of electrons field emitted at (202&#x0304;1&#x0304;) and (101&#x0304;1&#x0304;) demonstrates the non-free character of electrons in rhenium, while the small effect of adsorbed gold strengthens the belief that gold is bound through a greatly broadened 6s level centred 5.6 eV below the Fermi level and the dipolar nature of the bond supports this model. At higher values of T_s and $\text{}\text{?}$gq gold appears to form states which are well-characterised by a coverage-independent work function. (101&#x0304;0), (101&#x0304;1&#x0304;) and (112&#x0304;0) each form two such states, one in the range 2 < $\text{}\text{?}$gq < 4 (state 1), and the second at $\text{}\text{?}$gq > 4 (state 2). The atomic radii of gold and rhenium are thought to be sufficiently similar to allow the possibility that state 1 is a replication of the Re plane structure by gold. The high work function and thermal stability of state 2, taken together with the observed temperature dependence of the transformation of state 1 to state 2, encourages the belief that state 2 results from atomic rearrangement of state 1 into a close-packed Au(111) structure. State 2 also forms on (112&#x0304;2&#x0304;) and the absence of state 1 on this plane suggests some surface alloying at coverages below 4 $\text{}\text{?}$gq.     

The second and third order non-linear optical properties of liquid crystalline polymers

The second and third order non-linear optical susceptibilities of several donoracceptor substituted side chain polymers, some of which exhibit mesophases, will be reported. The susceptibilities were measured by harmonic generation from thin films, typically 0·5 μm thick, at a fundamental wavelength of 1064 nm and 1579 nm. For second harmonic generation, the spin coated films were contact poled on a glass substrate with an interdigited electrode pattern. Typical values obtained were χ⁽²⁾₃₁ = 1 × 10^-9 esu and χ⁽²⁾₃₃ = 3 × 10^-9 esu, the largest value was χ⁽²⁾₃₃ = 6·3 × 10^-9 esu. The difficulty in deriving reliable second order structure-property relations because of the large effect which the contact poling process has on the non-linear optical susceptibility of the films will be highlighted. The highest χ⁽³⁾ value of 5·8 × 10^-12 esu obtained from an amorphous film of a polymer with an asymmetrically substituted azo side group is comparable with the susceptibility of more typical third order non-linear materials such as the main chain polymers polyphenylacetylene and poly-p-phenylenebenzobisthiazole.     

Oscillation criteria for nonlinear second order equations

Summary A necessary and a sufficient condition are given for oscillation of all solutions of y″+f(t, y)=0. We sequire that a(t)α(y)≤f(t, y) if y>0, and f(t, y)<-b(t)β(y) if y<0, together with continuity and integrability assumptions on a, b, α, and β. Of speciat interest here is the relaxing of conditions a≥0, b≥0 in Machi - Wong [6]. Entrata in Redazione il 9 ottobre 1968. Supported by NASA Research Grant NGR-45-003-038.     

Experimental upper limits for hadronic and axion decays of the γ(1S)

A search for the decays γ→ρπ, γ→J/ψX and γ→γa (whereX is undetermined and a is an axion) has been completed using the LENA detector at the DORIS storage ring. No evidence for any of these processes was found. For these decay modes we set branching fraction upper limits (90% C.L.) of 2.1×10^?3, 2.0×10^?2 and 9.1×10^?4, respectively.     

Photomechanically induced ferroelectricity in smectic liquid crystals

We report new photomechanical effects in the ferroelectric liquid crystal SCE13 doped with a photoisomerizing guest azo dye. Low concentrations of dye (∼5 per cent wt:wt) are shown to cause an isothermal, reversible disruption of smectic phases when the system is illuminated with low power density (∼ 1 mW cm^-2) UV light. In the case of a sample initially in the S*_c phase, this results in a fall in the magnitude of spontaneous electrical polarization (P_s) and changes in electro-optic switching characteristics. If the sample is illuminated in the S_A phase, the electroclinic switching decreases. In contrast to this, when systems containing higher concentrations of dye (≥ 10 per cent wt: wt) are UV illuminated in the S_A phase, a reversible, isothermal transition to a biphasic S*_c/isotropic state occurs. In this case, the P_s is seen to rise from zero in the S_A phase to a finite value(∼2 nC cm^-2) in the biphasic mixture and hysteresis occurs in the electro-optic switching. When these higher dye concentration mixtures are held initially in the S*_c phase and UV illuminated, a more complicated variation of P_s occurs with the sample again undergoing a transition to a biphasic S*_c/isotropic state. Possible mechanisms for the transition are discussed.     

交通产业链上企业工程项目成本控制的影响因素研究

一些企业以轨道交通产业为纽带形成了交通产业链,轨道交通产业链上的企业要注重对相关工程项目实施全过程中的成本控制.从产业链的视角出发,围绕财务指标、内部业务流程指标、客户指标、学习与成长能力指标这4个方面,构建了评价指标体系和成本控制指标体系.运用层次分析法和模糊综合评价法进行评价和分析,找出了影响轨道交通产业链上企业工程项目成本控制的主要因素.研究表明,有55%的人认为财务指标、内部业务流程指标、客户指标、学习与成长能力指标这4个因素对轨道交通工程项目成本控制的影响较大.     

The Order-Disorder Phase Transition in Liquid Crystals as a Function of Molecular Structure. I. The Alkyl Cyanobiphenyls

The pretransitional behaviour of a homologous series of mesomorphic compounds, the alkyl cyanobiphenyls (CNρρC _n H _{2n + 1}) for n = 5–12, has been studied as a function of temperature by light scattering in the isotropic phase. The higher homologues, n = 8–12, exhibit a smectic A phase that becomes increasingly important at the expense of the nematic phase for increasing n and for n = 10 and 12 no nematic phase is observed. We have shown from light scattering and differential scanning calorimetry measurements that the presence of the smectic A phase changes markedly the pretransitional behaviour, and gives rise to two distinct pretransitional regions. The first region is for temperatures greater than ～3°C above the clearing temperature T_c where the systems exhibit a typical pretransitional behaviour adequately described by the phenomenological Landau-de Gennes model of a second order phase transition with an intervering first order transition at T_c . The constants of this model for this region are given and show a distinct odd-even effect. The second region is close to T_c where a strong divergence from the already critical behaviour is observed. This secondary divergence is observed to be a function of the alkyl chain length and its conformation, and is attributed to coupling between smectic A like layers and the orientational order parameter in the isotropic phase.